Diesel particulate filters (DPFs) are designed to remove soot from the exhaust flow of a diesel engine. When the accumulated soot reaches a predetermined amount, the filter is “regenerated” by burning off the accumulated soot. There is no mechanism available to directly measure the amount of soot in the exhaust flow from the engine, or the amount of soot in the DPF when the vehicle is in use. Accordingly, mathematical and empirical soot models have been used to estimate the amount of soot present in the DPF so that timely disposal or regeneration of the DPF can be assured. Modeling the exhaust flow and resultant DPF loading is dependent on complex chemical reactions and physical flow dynamics. Many models utilize multiple lookup tables and parameters, all of which require lengthy and labor intensive engine and vehicle testing and calibration work.
Accuracy of the soot model used is important, as the DPF functions optimally when the amount of soot present is below a predetermined amount. One soot loading model is dependent upon a pressure differential across the DPF. However, the measurement of the pressure differential is less accurate when the exhaust flow rate is relatively low. An accurate soot model ensures that the DPF is not regenerated unnecessarily at relatively low soot concentrations (grams of soot per volume of filter), thus enhancing fuel economy.